Heart transplant is a course of action for patients with end stage heart failure, a leading cause of premature death. Due to the unavailability of donor hearts, electromechanical blood pumping systems are being developed and are increasingly coming into use. These devices can provide a bridge to transplant, a bridge to recovery, or a permanent treatment for patients who may not receive a donor heart. Most of these patients will be treated with a ventricular assist device (“VAD”), which assists the beating heart by drawing blood from the left or right ventricle and discharging the blood to the aorta or pulmonary artery, respectively. Some patients require a total artificial heart (TAH), which replaces the patient's heart, as a bridge to transplant or as a permanent therapy.
One known type of TAH is a continuous flow total artificial heart (CFTAH). The CFTAH includes two centrifugal pumps on one rotor supported on a hydrodynamic bearing and driven by a single motor. The CFTAH replaces the ventricles of the heart, and delivers blood flow to both the systemic (left) and pulmonary (right) circulation of the patient. Examples of CFTAH pumps are described in U.S. Pat. No. 8,210,829 B2 and U.S. Pat. No. 7,704,054 B2, and in U.S. Patent Application Publications US 2010/0174231 A1 and US 2012/0328460 A1.
CFTAH implementation can be performed by surgically excising the ventricles and connecting the left and right pump inlets to the left and right atria, respectively, and connecting the left and right pump outlets to the aorta and pulmonary artery, respectively. During the operation of the CFTAH, care must be exercised to avoid a suction condition in which atrial tissue is sucked into the pump inlet, thereby blocking flow into the pumping chamber and causing an imbalance in systemic and pulmonary blood flow. In addition to the obvious physiological problems brought on by this condition, suction conditions can lead to the pump rotor shifting axially onto a thrust bearing which can lead to hemolysis and/or thrombosis.
While this type of CFTAH can be operated under external control, it is desirable for the system to respond automatically to physiologic changes, preferably using the least number of sensors. Additionally, in the physiologic control scheme, there is a need to detect conditions, such as tissue suction at the pump inlets, that may jeopardize the patient.